As much as possible I try to make it obvious from a variable label, what type of variable it is and wherever possible, what other variable or control block it is related to.

Constants

I start variable names for constants with a # sign, thus:

#NAME DC C'NAME'

If a variable starting with a # sign is on the receiving end of an instruction, it is wrong because I should not be modifying constants!

Equates

I start equated value names with an @ sign, thus:

@ONE EQU 1
@FLAG1 EQU X'80'

For equated symbols that define a length, I add the suffix ‘_LEN’ to the symbol name, thus:

FIELD1 DS CL8
@FIELD1_LEN EQU *-FIELD1

That way, it is obvious in the code that I am referring to an equated length value, for example:

LA R1,@FIELD1_LEN Get field length in R1

It it obvious that I intend to load the field length and not the field address into the register but having the _LEN suffix ensures that I get the length and do not accidentally code the field address instead.

Equate/Field relationship

I prefer to ‘tie’ equated values for a field to the field they relate to by using a naming convention that uses the field name as part of the equate symbol, thus:

Similar code would apply to setting the field value, only use equated symbols that are related to the target field. This convention ensures that you are only setting and testing for values actually defined for the field.

About the only exception to this rule that I use is the use of the following common equated symbols:

@YES EQU C'Y'
@NO EQU C'N'
@POSTED EQU X'40'

@YES and @NO should be obvious, @POSTED is to test an ECB posted bit flag,E.G:

TM ECB1,@POSTED Is ECB posted?
BO DONE

Field/DSECT relationship

When I am creating my own DSECTS I prefer to prefix the name of each field within the DSECT with the DSECT name and an underscore, thus:

Using this standard makes it easy when reading source code to determine who owns a field. There is no confusion. The length equate for the control block also follows my convention of adding _LEN to the end and prefixing the equate symbol with an @ sign to avoid ambiguity in the executable code.

The exception to the rule…

I do allow for one exception to this rule though and that is for a program’s working storage. Typically I prefix working storage fields with the prefix STG_ (short for ‘storage’) although you can use anything you want, to identify working storage fields, for example W_ etc. It is preferable to use the underscore as part of the name to avoid situations where a field name ‘might’ happen to start with whatever prefix you are using. For example if you use just W as your working storage field prefix, is WORKF1 a field in your working storage or somewhere else? Using this convention, STG_WORKF1 or W_WORKF1 are obviously part of the code’s working storage. And again, the convention ensures that you are using the field you intend and not a WORK1 field defined somewhere else that might allow the program to assemble but my then fail at execution time because the storage it refers to is not addressable or it is addressable but it’s the wrong field and messes up some other code (good luck finding that one!).

Summary

Whatever conventions you use, the aim is to make it less likely to introduce errors when developing the code and to make it much easier to read, and locate field owners several months later when someone else has to try to follow, understand and debug or modify your code.

There are probably as many ways to write a program as there are programmers in the world, more if you accept that a program is solution or part thereof, to a problem and could be written in more than one language, each of which causes the writer to adopt differing styles.

So basically, there’s more than one way to skin a cat!

Now I’m not saying that the style of assembler programming that I have developed over the years is the best but I think it satisfies many of the requirements that I will cover in what I hope will be a short series of articles. Let’s put it this way, unless someone tells me different, I’ll tend to try to influence any code that I work in towards my preferred style although there are reasons for NOT doing that, for example to maintain the existing style or coding standards since a mix can make things worse.

SO! Why is style important?

Sometimes it isn’t. You may need to write a quick, one off, one use program to solve a problem. As long as it does the job, does style really matter? Well, it depends. If the code is simple then probably not but what if the code is complex? Then making the code at least readable and logical makes sense since if you get it wrong the first time through, it will be a lot easier to diagnose the problem and correct the code.

But let’s consider the more common situation where you are developing a program or even multiple programs that form a piece of software and those programs are for use by paying customers. In other words you are creating commercial software. I am also including software written for in house use (in the business sense) because such development, use and support usually involves internal billing and thus still qualifies it as commercial software.

Basically, if someone else other than the developer or developing department uses it, you can consider it to be commercial software in my mind.

So let’s say that you are assigned the task of developing a z/OS super widget application which, because it uses lots of system services will be written in assembler, or at least a lot of it will be. Let’s looks at how programming style will affect it’s life cycle.

Development

The faster you can develop and test the code to the point where it does what the requirements require without failing or causing other problems, the faster the product will reach the market and thus generate revenue for the business.

Everyone probably has a standard program entry and exit macro and possibly similar ones for subroutine entry and exit but what about other stuff. Parsing of input for example? Do you do it with hard coded assembler or use a macro or service to do parsing in a standard and consistent manner? If a service, do you call that service using a macro to make coding the call simpler and standard? Or, do you let your programmers set everything up by hand (guess which is the more reliable method)?

Do you use a standard form of label name for program labels and subroutine names? Are you still stuck in the ‘all labels must be 8 characters long’ mental state or do you use longer and more meaningful names, either CamelCase or with parts separated by underscores, E.G. WORK_FIELD_1.

Do you use naming standards to tie equated symbols to the field they relate to or is it a free for all. Is it easy to tell, without looking at the variable definition, if a variable name is a label or an equated value and if a label, is it easy to tell which control block it belongs to, or if a constant, is it easy to tell that it is a constant?

And most importantly in my mind, do you create comment blocks for the program as a whole and for each subroutine that describes the program, it’s inputs, outputs and return codes and the same for all subroutines? Also, if the program is reliant upon a particular control block structure, do you document that WITHIN the code as best you can (using good old EBCDIC character graphics if need be) so that the architecture is right there in the code, not lost on some hard drive somewhere that got wiped because someone didn’t realize that what was on it was needed (the ‘not my job’ syndrome!).

Maintenance

If the code is well structured, follows consistent naming standards, uses macros to standardize the coding of interface, has proper comments describing what each routine does, what it’s input and outputs are then understanding the code and diagnosing a problem becomes a lot easier and more importantly faster. You are also more likely to be able to correctly fix any problem without introducing new problems. All the above result in a faster turn around time for the resolution of any code related problems. They also mean it is much easier for someone other than the original developer to pick up the code and work on it with confidence.

This all results in improved customer confidence in the product and better tolerance for any problems that do occur because they know that they can be quickly resolved.

New Features

Code that is well structured is much easier to modify to add new features to. And just like the maintenance situation, there is less likelihood of such changes introducing new problems into either the new or the existing code. This all helps to get the product out to market that much quicker and earning revenue.

The Bottom Line

If you are a commercial programmer, that is, it’s your job, your work earns the business that you work for, the money that pays your wages. The quicker you can develop new code or fix existing code directly affects the companies business results and therefore your earnings.

Back in the day when dinosaurs still roamed the earth and programmers still knew how to use a card punch, there were printers. Not your desktop printer of today but huge big, noisy things with all the characters on a chain, a ‘ribbon’ as wide as the paper that fed vertically on rollers and a a row of hammers that stuck the correct character as it went past on the chain, if you got it setup right that is! These things also used a paper loop for carriage control that told it where various spots where on the page, in particular the top of the page. Happy days!

In those days your program listing got printed out, so to make it more readable you’d put EJECT statements into the source code, usually before a subroutine so that the subroutine and all the comments about what it did, its inputs and outputs etc; (you did document all that stuff didn’t you?) were at the top of a page.

Fast (or not) forward to today and I doubt anyone actually prints program listings anymore. If you are anything like me it’s all online, either in SDSF, sent to a member of a ‘listings’ dataset or, if your source is off platform, your tool set grabs the output after the assembly has run and FTPs it back to your workstation/PC where again, you can view it online.

So, since the output is now all just one big stream, why would you bother putting EJECT statements into your source, other than from habit?

Now I will admit that I did this from habit until I got to thinking about it (hence this post!) and there is actually a very good reason to include EJECT statements in your source, especially before the start of a subroutine.

In this code, I have let the using for WSA in the main line code ‘fall through’ into the sub routine (something I normally hate to do except for working storage based on R13). The only way you can tell that the LA,R1,FIELD1 instruction in the subroutine is using R2 as a base register for WSA is by looking at the assembled instruction.

The difference is that you now get one or more lines (depends on how many usings are active) that show the current usings in effect at the very start of the subroutine. As a result I can see exactly which usings are active and whether I have inadvertently ‘inherited’ one from an earlier routine that should have been dropped.

As a matter of coding style, I prefer to always drop all active usings, including code base regs except for working storage that is based on R13, at the end of each routine. That way I
know I am using the correct registers and usings in each routine and by putting an EJECT statement in the source before each routine, I can easily see from the listing that I am not inadvertently inheriting a using from an earlier block of code that may allow the code to assemble but ultimately fail when it runs because I picked up the wrong base register.

Since I’m a mainframe guy I’ve spent most of my career writing REXX whenever I needed a quick script which means that I know REXX pretty well. Lately I’ve been playing with REXX on Windows thanks to an implementation of REXX called Regina Rexx, see here.

Of course, one of the things you can do on Windows is drag and drop so I wanted to be able to drop a file onto a Regina REXX program and have the REXX program then process the file.

Typically you access input parms in a REXX exec by using the “parse arg varname” statement but I found that this did not work when dropping a file onto a Rexx exec on my Windows machine.

After some research I found that I needed to create a shortcut to the Regina REXX.EXE program with a parameter that is the path and name to the REXX program to run. You then have to drop your files onto the SHORTCUT.

So let’s say I have the following exec called “test.rexx” on my desktop:

If you’ve ever read or written a macro you have no doubt at least seen conditional assembly language. It’s all that AIF and AGO stuff that forms a sort of ‘program’ within the macro so that it can generate code or whatever depending on whatever the input parameters are.

What’s really cool though is that it is not just limited to macros, you can use it within open code as well. So you might ask ‘why would you need to do that?’ but even if you don’t ask, here’s one interesting situation that came up recently.

I had some code that used a macro to generate a DSECT to map a control block. However we were switching version of the product that supplied the macro and a field within the macro had changed names even though it’s content had not. The result was that my code would only assemble with one version of the macro since with the other one it would get a not found error for the changed label. Since I did not want to have to co-ordinate my source code change with a build tool change the problem I had was how to make my source code support both versions of the macro and DSECT that it generated?

In case you have not guessed, the answer is conditional assembly language.

Here’s an example.

The old macro/DSECT:

MYMACRO
SOMENAME DSECT
MYFIELD DS CL8

The new version of the macro/DSECT

MYMACRO
SOMENAME DSECT
NEWNAME DS CL8

So my code originally looked something like this:

USING SOMENAME,R2
CLC MYFIELD,=CL8'AAAAAAAA'

Obviously if I switch to the new macro library, my assembly will fail since the field ‘MYFIELD’ is no longer defined within the DSECT.

However, what you can do is to test to see if the variable ‘MYFIELD’ is defined and if not then conditionally change the code that gets assembled. Thus:

The AIF tests to see if the ‘type’ specification for the field MYFIELD is ‘U’, that is undefined. If it is undefined that means it has not been seen by the assembler (yet) so jump to the label .NEWMAC and continue to generate the code from there, which of course generates the code using the new field label of NEWNAME.

If the field MYFIELD is not ‘undefined’ then the assembler generates the code using the old field name, MYFIELD and then jumps (AGO) to the label .CONT to continue the assembly.

As a result, no matter which version of the macro library I am using, my code still assembles and works correctly.

There are other ways of achieving the same effect; For example by using the conditional assembly language to control the redefining of the old or renamed symbol to a common name and using that common name in the open code.

One gotcha though to be aware of. The macro/DSECT has to be defined in the source code BEFORE the conditional assembly code. If it is defined after the conditional code then, since the assembler has not seen either field at the time it encounters the test for the field being defined, it will always treat it as being undefined which would cause an assembly error when using the old macro/DSECT library because it would generate the code to use the new field name.